The invention relates to a thin-film capacitor comprising an electrically insulating substrate which is provided with at least two inner electrodes which are separated from each other by means of a dielectric layer, and with two end contacts which each electroconductively contact one of the inner electrodes.
A thin-film capacitor of the type mentioned in the opening paragraph is known per se, for example from U.S. Pat. No. 4,453,199. Said patent document more particularly describes a thin-film capacitor which is provided with an electrically insulating substrate which is preferably made of glass. Said glass substrate is provided, by means of thin-film techniques, with successively a sub-layer of phosphor-doped silicon dioxide, a first inner electrode of aluminium, a dielectric layer of silicon dioxide, a second inner electrode of aluminium and an overlayer of silicon dioxide. The known capacitor is further provided with two sputtered end contacts. Via one of the ends, each of the inner electrodes electrically contacts one of the end contacts of the capacitor.
It has been found that the known thin-film capacitor has an important drawback. It has namely been found that in the case of mass-production of the known thin-film capacitor, the value of the contact resistance between the end contacts and the inner electrodes is relatively high. In addition, it has been found that this value is not the same for all capacitors manufactured in a single batch. This relatively high and variable value of the contact resistance may cause problems in high-frequency applications of this type of thin-film capacitor. Under said conditions, the contribution of the contact resistance to the ESR (electrical series resistance) becomes unacceptably high. The value of the ESR is determined by the resistance of the inner electrodes, the resistance of the end contacts and by the contact resistance between the inner electrodes and the end contacts.